A control device including an electronic device such as circuit board is accommodated in a housing is used for operation control of all machines irrespective of its purpose or intended use. In a vehicle as well, many control devices are used for controlling in-vehicle devices such as an engine, a transmission, a brake, and an airbag. It goes without saying that normal functions are generally required for these control devices so that the machines, to which they are attached, can successfully operate. However, in the control device disposed in the vehicle, the function of the electronic device needs to be maintained not only when the vehicle is in good condition but also at the time of collision of the vehicle. Particularly, the control device that performs operation control for a body protective device such as an airbag needs to function normally in order to activate the body protective device even if the vehicle is deformed after the collision. In addition, recently, an event data recorder (EDR) that records the data before and after the collision of the vehicle is incorporated in the control device that carries out operation control of the airbag. In order to acquire the date, the control device needs to operate normally for at least a predetermined time even after the actuation of the body protective device.
As a measure against such an issue, there is a conventional art concerned with a control device that is configured to avoid the stress generated at each part of the vehicle after the collision of the vehicle so as to maintain its function normal (see, e.g., JP2002-308021A). This device is a control device including a plate material, to which a circuit board is attached, and a case attached on the plate material to cover the circuit board. Brackets project from the outer peripheral surface of the case, and the control device is fixed to the vehicle by bolting the brackets to the vehicle body. A thin wall part is formed on the lower end surface of the case. When a strain is caused at the vehicle body at the time of the vehicle collision, a breaking is caused at the thin wall part due to the load applied to the case. Accordingly, the applied strain is absorbed by the breaking of the thin wall part. As a result, the circuit board is not affected, thereby maintaining the normal operation of the control device.
As described above, in the case of the control device of the conventional art, the strain caused at the vehicle body is absorbed, for example, by breaking the thin wall part, to which the load is applied. However, there is an issue that the amount of strain for breaking a material of the case varies considerably and that the characteristics for avoiding an impact of the collision are thus not stabilized according to the above-described conventional art. In particular, the case is often formed by aluminum die-casting or the like, and its strength may also vary according to, for example, a casting cavity or pinhole contained.